There is a need for improved plasma thrust generators or thrusters for controlling the orientation and maneuvering of small power-limited satellites in space of 100 watts or less. These small satellites are expected to be widely used for Air Force and commercial applications. Such attitude control thrusters should be packaged in small lightweight containers and be highly efficient so as to employ small amounts of power, typically less than 100 watts.
Pulsed power thrusters (PPTs) are presently commercialized for use on small power limited satellites which employ solid inert propellants such as "Teflon" polymer. An energy storing capacitor, charged up in about a second, is rapidly discharged in about 10 microseconds at high instantaneous power to vaporize the propellant and produce thrust. The solid propellant eliminates the engineering complexity associated with prior art gaseous propellants, and is converted to vapor and is partially ionized by a surface discharge. Acceleration is accomplished by a combination of thermal and electromagnetic forces to create usable thrust.
The problem with these prior art PPTs is that typical thrust efficiencies for flight models are generally about ten percent or less. The low thrust efficiency is attributable to both low propellant efficiency and low energy efficiency. Further research has shown that energy used to create the magnetic field that accelerates the plasma is poorly used, and significant resistive diffusion of the magnetic field into the plasma is observed. The magnetic energy associated with this field is diffused into the plasma as heat, creating minimal thrust through thermal acceleration.
Propellant conversion is initiated through a surface discharge, and sustained through soft X-ray deposition from the plasma arc, initiated by a sparkplug igniter, and a significant portion of the resulting radiative energy is deposited too deep in the propellant to be used in the discharge. This energy preheats the propellant bar and decreases the propellant efficiency, and energy used to break the strong bonds of the Teflon polymer is unavailable to produce thrust. Also, the mass and energy of the igniter circuit decreases energy efficiency and increases dry mass. Additionally, the plasma component in the PPT has an excessive velocity, and it would be preferable to increase the mass of the plasma component to increase thrust, at the expense of exhaust velocity.
Thus, it is desirable to provide a more capable, low mass, thruster of less than 100 watts, and at reduced cost. It is also desirable to provide a thruster consuming less propellant for a given satellite maneuver.